package com.zcc.servlet;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.nio.charset.StandardCharsets;
import java.util.Random;

public class ImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //让浏览器3s自动刷新1次
        resp.setHeader("Refresh","3");

        //在内存中创建一个图片
        BufferedImage bufferedImage = new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB);
        //得到图片
        Graphics2D graphics = (Graphics2D) bufferedImage.getGraphics();
        //设置图片的背景颜色
        graphics.setColor(Color.WHITE);
        graphics.fillRect(0,0,100,20);
        //给图片写数据
        graphics.setColor(Color.BLUE);
        graphics.setFont(new Font(null,Font.BOLD,20));
        graphics.drawString(makeNum(),2,20);

        //告诉浏览器，这个请求用图片的方式打开
        resp.setContentType("image/jpeg");
        //网站存在缓存，不让浏览器缓存
        resp.setDateHeader("expires",-1);
        resp.setHeader("Cache-Control","no-cache");
        resp.setHeader("Pragma","no-cache");

        //把图片写给浏览器
        ImageIO.write(bufferedImage,"jpeg",resp.getOutputStream());
    }

    private String makeNum() throws UnsupportedEncodingException {
        //创建最大7位整数的随机数
        Random random = new Random();
        String num = random.nextInt(9999999)+"";

        //如果不足7位，用0填充
        StringBuffer sb = new StringBuffer();
        for(int i=0;i<7-num.length();i++){
            sb.append("0");
        }

        //把随机数和填充用的0字符串合并
        num = sb +num;
        return num;
        //return new String(num.getBytes(StandardCharsets.UTF_8), StandardCharsets.UTF_8);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}
